When performing synchronous transfer (isochronous transfer) of data between nodes, a transmission channel and a transfer band can be acquired by an isochronous resource manager (IRM). The usable transfer band is managed by referring to a band indication register included in the isochronous resource manager.
Referring to FIG. 6, a band management operation performed by referring to the band indication register will now be described. An isochronous resource manager includes, for example, eight-bit band indication registers 1. In the band indication registers 1, FFh (in which h expresses a hexadecimal number) is set as an initial value for a data transferrable band value.
In this state, when node 1 acquires a transfer band of 0Fh in transmission channel ch1, the residual band indicated by the band indication register becomes F0h. Then, when node 2 acquires a transfer band of 10h in transmission channel ch2, the residual band indicated by the band indication register becomes E0h. Then, when node 3 acquires a transfer band of 20h in transmission channel ch3, the residual band is further indicated by the band indication register.
In this state, even if a further node attempts to acquire a transfer band, the residual band indicated in the transferrable band is less than F0h. Thus, the further node cannot acquire a transfer band, and data transfer cannot be performed. The band indication register 1 only indicates the usable transfer band and does not function to control the transfer band.
Referring to FIG. 7, the transfer operation of the nodes 1 to 3 that acquired transfer bands as described above will now be discussed. One cycle of the transfer operation, that is, the transfer interval of cycle start packets CS is 125 μs. In a manner following the first cycle start packet CS, the data of node 1 is transferred in the 0Fh band of channel ch1, which is allocated to node 1. Then, the data of node 2 is transferred in the 10h band of channel ch2, which is allocated to node 2. Then, the data of node 3 is transferred in the 20h band of channel ch3, which is allocated to node 3.
In such a transfer operation, the bands acquired in channels ch1 to ch3 do not increase or decrease in correspondence with the data amount during data transfer. For example, as illustrated in FIG. 8, the data that is to be transferred by node 3 in channel ch3 is compressed prior to transfer. This reduces the data in size and narrows the band required for transfer. In this case, the transfer band for 20 h has already been acquired for channel ch3. Thus, an unused band may remain in the transfer band of channel ch3. The unused band lowers the transfer efficiency.